H. Farhangfar, H. Naeemipour Younesi,
Volume 11, Issue 1 (4-2007)
Abstract
A total of 25,471 Iranian Holstein heifers distributed in 523 herds of 20 provinces were used to estimate heritability, genetic and phenotypic associations between a number of traits related to the production and reproduction performance. The Animal Breeding Centre of Iran collected the records studied in this research between 1991 and 2001. The traits associated with production were 305-day, 2x adjusted milk, fat yields and fat percentage and the traits associated with reproduction were age at first calving, number of services per conception, gestation period, calving interval as well as dry days as a separate trait. The heritability estimates were 0.31, 0.23, 0.31, 0.14, 0.03, 0.05, 0.10 and 0.01 for 305-day, 2x milk, fat yields, fat percentage, age at first calving, dry days, calving interval, gestation period and the number of services per conception, respectively. Milk yield was genetically correlated with age at the first calving (-0.14), dry days
(-0.31), calving interval (0.54), gestation period (0.01) and the number of insemination per conception (0.38). Fat yield had negative genetic correlations with age at first calving (-0.16), dry days (-0.23) while it was positively correlated with calving interval (0.44), gestation period (0.11) and the number of insemination per conception (0.20). Age at the first calving, dry days and gestation period had a positive genetic correlation with fat percenateg (0.03, 0.15 and 0.09 respectively) while calving interval and the number of insemination per conception were negatively correlated with fat percentage (-0.21 and -0.25 respectively).
S Shrifi, H Rahmani, M Motamedi,
Volume 13, Issue 47 (4-2009)
Abstract
In dairy cattle, the increase in milk yield has been accompanied by a more negative energy balance during early lactation and a decrease in fertility. The 167 amino acid protein product of the ob gene was named leptin (derived from the Greek term ‘leptos’ meaning thin). The leptin hormone, as a 16-kDa protein is synthesized mainly by adipose tissue and is involved in regulation of food intake, energy balance, fertility and immune function. The expression and secretion of leptin are correlated with body fat mass and are acutely affected by changes in food intake. The objective of this study was to investigate the fluctuations of leptin concentrations during late pregnancy and early lactation, the effect of parity and BCS on plasma leptin concentration, and to investigate its fluctuation effects on reproductive status. Blood samples of 54 Holstein cows were taken at a fixed time of the day after milking but before feeding, from 2 weeks before calving until 6 weeks after calving. BCS and plasma leptin concentration were measured at 2-wk intervals. Leptin concentrations were affected by parity. Primiparous cows and cows in first parity had higher leptin concentrations compared with multiparous cows (P<0.05). Leptin concentration was not different in late pregnancy and early lactation. BCS was negatively correlated with plasma leptin concentration (P<0.05). Plasma leptin concentration did not influence reproductive traits (days in milk at first breeding, service per conception and open days).
